Magnetic properties of arrays of cobalt nanoparticles on the CaF2(110)/Si(001) surface

Autor: D. S. Il’yushchenkov, N. S. Sokolov, A. K. Kaveev, S. V. Gastev, B. B. Krichevtsov
Rok vydání: 2009
Předmět:
Zdroj: Physics of the Solid State. 51:118-126
ISSN: 1090-6460
1063-7834
DOI: 10.1134/s1063783409010156
Popis: The Co/CaF2/Si(001) heterostructures with the corrugated (110) surface of the CaF2 buffer layer have been grown by molecular beam epitaxy. The structures are nanoparticle arrays of single-crystal Co, mostly of the cubic fcc modification. The behavior of the magnetic hysteresis loops as a function of the density of coverage of the substrate by cobalt islands, the island size, and the temperature is studied using the magnetooptical technique. At low coverage densities, where the effective cobalt film thickness deff is less than the critical value deffc, the magnetic structure of the films at T = 294 K can be visualized as an ensemble of superparamagnetic, weakly interacting nanoparticles and is characterized by small values of the coercive field Hc and the remanent magnetization Mrem. A decrease in the temperature leads to a strong increase in Hc and Mrem, which is associated with the transition of the islands to the blocked state. The blocking temperature of the structures is Tb ∼ 280 K. The magnetic anisotropy parameter K and the saturation magnetization Ms of the islands depend on the growth temperature of cobalt TCo. An increase in the coverage density above the critical thickness diffc at T = 294 K brings about a strong increase in Hc and Mrem and the appearance of a hysteresis loop anisotropy originating from the corrugated structure of the CaF2 buffer layer. The experimental results are compared with the model of an ensemble of noninteracting superparamagnetic particles.
Databáze: OpenAIRE
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